The present invention relates to a fog-producing apparatus and more particularly pertains to a versatile, low-maintenance fog generator that can be used for a variety of applications including the creation of theatrical or visual effects.
A number of methods have heretofore been employed for suspending a finely divided liquid in a gas. Disadvantages associated with these methods limit their utility. For example, steam producing techniques consume significant amounts of energy and may pose a safety risk due to the associated elevated temperatures and pressures involved. High pressure nozzle systems use a combination of low pressure liquid and high pressure gas to generate a large particle mist. Substantial volumes of compressed gas are required and the typically high muzzle velocities can pose a danger. In addition, the small diameter nozzles clog easily and thereby compromise the performance of such a system. Cryogenics (i.e. liquid nitrogen and liquid carbon dioxide) can be dangerous to handle and are prohibitively expensive.
When only the appearance of fog or mist is required so as to produce theatrical or visual effects, additional methods are applicable as for example the combustion of a smoke-producing material, the use of a chemical fog or the suspension of solid particulates in the atmosphere. Significant disadvantages are associated with each of these methods when used in a theatrical environment especially when the effect is to be maintained or continually repeated over an extended period of time. Combustion invariably requires heat and flame, emits potentially hazardous combustion products and consumes the combustible material. Chemical fog typically has a distinct odor, leaves an oily residue behind and is of significant cost. Solid particulates, such as for example finely divided flour leaves a messy residue and is relatively expensive. In addition, the previously mentioned steam producing technique can quickly raise the ambient temperature and humidity of a theatrical set to uncomfortable levels, while the cyrogenics approach, due to the cold gases' inherent densities, may not provide quite the desired effect.
An alternative approach devoid of the disadvantages listed above employs an ultrasonic transducer. Such a device consists of a ceramic, stainless steel coated disk which is caused to oscillate in the MHz frequency range by an electric signal generated by associated electronic circuitry. The resulting high frequency shock waves produced by the transducer are transferred through the liquid with which the transducer is in contact to the gas/liquid interface where the intermolecular bonds of the liquid are mechanically overcome. Atomization of the liquid is thereby accomplished as the molecules are ejected in small clusters and become suspended in the gas. Such a device when adapted for use within water produces a true fog devoid of odor, poses no health or safety hazard, does not present residue or contamination problems, does not significantly affect the ambient temperature of its environment and is capable of producing substantial volumes of fog or mist at a very modest cost. Such transducers are adaptable for use in any non-viscous liquid.
The major disadvantages and shortcomings associated with the use of MHz transducers to produce a mist or a fog have heretofore related to the leakage of liquid into sensitive areas of the transducer and its associated circuitry in addition to problems associated with effectively maintaining the critical liquid level above the transducer disk. Given a certain disk size, power output and operating frequency of a particular ultrasonic transducer determines the optimum depth of liquid that needs to be maintained over the transducer to maximize the fog output of such a device. This requirement has typically been filled in a relatively complex manner by disposing the transducer beneath a body of liquid and maintaining a predetermined liquid level thereabove with a float and valve arrangement.